The invention relates to a process for treating a particulate material, in which, in a container which has a base, an upright wall that widens from bottom to top, and in the upper region a deflection element that adjoins the wall, the material is moved in a Continuous circulatory movement along the base to the wall and along the wall as a result of rotation of the wall upward about a vertical axis of rotation and is deflected at the deflection element in such a way that it can pass back to the base.
The invention further relates to an apparatus for treating a particulate material, comprising a container which has a base, an upright wall that widens from bottom to top, and in an upper region a deflection element in order to deflect the direction of movement of the material moved upward along the wall in such a way that it can pass back to the base again, it being possible for the wall to be driven in rotation about a vertical axis of rotation.
The treating of a particulate material can consist in treating the material with a covering medium, in particular for coating medical, nutritional, industrial or chemical articles.
A process and an apparatus of the type mentioned at the beginning are used, for example, in the pharmaceutical, chemical, confectionery or foodstuffs industry. In the pharmaceutical industry, by means of sugar coating, medicaments are produced which are covered with a sugar syrup. By means of film coating, film or varnished tablets are produced, which is also understood to mean medicaments coated with a polymer.
In the apparatus and the process known from WO 00/10699, the particulate material is put into the container and, as a result of rotation of the wall of the container, is moved in a continuous circulatory movement along the base and the upright rotating container wall from a lower region into an upper region of the container, is deflected by a deflection element in the upper region of the container and is moved back again along an internal return surface spaced apart radially from the first container wall to the likewise rotating base of the container.
The deflection element, which is provided with a plurality of guide vanes, is firmly connected to the container wall and accordingly corotates at the same rotational speed as the wall of the container.
A further apparatus of the generic type is disclosed by DE 101 04 184 Al. This differs from the known apparatus described previously in that the return surface for feeding back the particulate material to the base of the container is arranged outside the upright wall of the container, which can be set rotating. In addition, the container of this known apparatus has in its upper region a deflection element in order to deflect the movement of the material, rising upward along the wall as a result of rotation of the upright wall, in such a way that it can pass back to the base of the container along the return surface arranged radially outside. In this known apparatus, the deflection element is static, that is to say it does not corotate during the circulatory movement of the particulate material.
Furthermore, WO 00/16887 discloses an apparatus for drying pourable products, comprising a rotor chamber, in which there is arranged a container rotating about a vertical axis of rotation, the container having a central horizontal surface and, at least in its radially outer third, a conical periphery, the conical periphery having at least partially two-dimensional gas passages in the form of perforations or screens. Through the gas passages, a dry gas is fed two-dimensionally into the conical periphery to the products to be dried during their radial peripheral circulation, without said products being swirled in the process and being subjected to impermissible pressure, shock and/or frictional loading. Above the conical periphery forming the wall of the container there is a deflection element which is provided with guide vanes which have the form of a segment of a spiral.
The known apparatuses and processes are disadvantageously suitable only for treating that material which consists of relatively large particles, for example of tablets and the like. The known apparatuses and processes are less suitable for treating material which consists of very small particles, for example pellets. In particular during the movement of the particles of the material along the deflection element, high braking forces act on the particles, which have a corresponding abrasive action on the particles. In the case of particularly small particles, this can rapidly lead to the destruction of the particles. On the other hand, in the case of small particles, it is possible that, on account of their low mass and therefore low kinetic energy which they can pick up because of their centrifugal upwardly directed movement resulting from the rotation of the wall of the container, they are not deflected reliably at the deflection element.
Blowing air in through a perforation in the rotating wall of the container, as in the apparatus and the process according to the aforementioned WO 00/16887, is likewise not suitable for the treatment of a material composed of very small particles, since the edges of the perforations firstly likewise have an abrasive action and secondly an air feed at a corresponding pressure is required in order to avoid the small particles escaping from the container through the perforations during their treatment. Increasing the blowing pressure would automatically entail a considerable increase in the quantity of process air and would swirl the particles, but this is precisely not desired in this type of process. Accordingly, the perforations would have to be configured to be of very small diameter, as a result of which, however, sufficient air cannot be fed into the container, in particular to adequately dry the particles of a treatment with a moist covering medium.
For these reasons, pellets are currently produced and treated virtually exclusively in what are known as fluidized bed apparatuses, in which the material is fluidized by an air supply from the base of the container but not circulated on account of a centrifugal movement resulting from rotation of the container wall.